1. Field of the Invention
The present invention relates to a method and device for driving a plasma display panel (PDP).
2. Description of the Prior Art
It is desired for a display device utilizing a PDP to realize a brighter display with lower electric power, i.e., to improve light emission efficiency. It is more preferable industrially to devise a drive pulse waveform for improving light emission efficiency rather than changing a panel structure including properties of fluorescent materials and composition of a discharge gas.
In a display using an AC type PDP, an addressing process is performed so as to control wall charge quantity of each cell of a screen in a binary manner in accordance with display data, and then a sustaining process is performed in which a sustain pulse is applied to all cells at one time. In the addressing process, it is decided whether the cell is lighted or not. In the sustaining process, light emission quantity is determined.
In the conventional driving method, during a display period for the sustaining process, a sustain pulse having a simple rectangular waveform is applied to a pair of display electrodes alternately. In other words, first and second display electrodes are biased to a predetermined potential (a sustain potential Vs) temporarily and alternately. In this way, a pulse train having alternating polarities is added between electrodes of the display electrode pair (i.e., to an XY-interelectrode). Responding to the application of the first sustain pulse to all cells, display discharge is generated in the cell in which a predetermined quantity of wall charge has been generated in the just previous addressing process. At that time, a fluorescent material in the cell is excited by ultraviolet rays emitted by a discharge gas and emits light. The light emission due to the display discharge is called “lighting”. When the discharge is generated, the wall charge on a dielectric layer is once erased, and reform of wall charge is started quickly. The polarity of the reformed wall charge is opposite to the previous one. Along with the reform of the wall charge, cell voltage at the XY-interelectrode drops so that the display discharge is finished. The finish of discharge means that discharge current flowing in the display electrode becomes substantially zero. When a second sustain pulse (a sustaining voltage) is applied, since the polarity of the sustaining voltage is the same as the polarity of the wall voltage at that time, the wall voltage is added to the sustaining voltage. Therefore, the cell voltage increases, and display discharge is generated again. After that, display discharge is generated by each application of the sustain pulse similarly. In general, application period of the sustain pulse is approximately a few microseconds, so that the light emission is viewed continuously.
For the application of the sustain pulse, a pulse circuit is used that has a push-pull structure with a combination of switching elements (usually, field effect transistors: FETs). The switching elements are arranged between each display electrode and a bias power source terminal, as well as between each display electrode and the ground terminal (GND). Each of the switching elements is turned on and off so that a potential of each display electrode is determined. However, in the control of the pulse circuit, a dead time is provided in which both switching elements are turned off in switching the potential. This is for preventing the bias power source terminal and the ground terminal from making short circuit and breaking down the switching element. During the dead time, each display electrode is separated from the driving circuit electrically. Therefore, just before the leading edge and the trailing edge of the sustain pulse in which a potential of each display electrode changes, the output terminal of the driving circuit becomes high impedance to the display electrode, so that current is suppressed between the display electrode and the driving circuit.
In the conventional driving method of applying a sustain pulse having a simple rectangular waveform as explained above, amplitude of the sustain pulse is increased within an allowable range so that intensity of the display discharge is increased, thereby light emission luminance is raised. However, if the luminance is made to rise, power consumption is increased and the light emission efficiency drops.